Chronic Total Occlusion (CTO) is an arterial vessel blockage that impedes proper blood flow beyond the obstruction. Poor blood flow can lead to insufficient delivery of blood to muscles and vital organs. CTO can occur both in the coronary and peripheral arteries, resulting in disability and even death. The underlying cause of CTO is atherosclerosis.
In order to reverse the effects of CTO, proper blood flow must be reestablished. This must be achieved by either driving through and removing the CTO or creating a bypass around the CTO. Under either scenario, the first step is to “cross” or drive a guidewire through or around the CTO. If the occlusion is relatively new, the plaque is likely to be soft and the guidewire will penetrate and cross the plaque. Thereafter, balloon angioplasty and stenting can be performed. However, if the plaque has been lodged in the vessel for several weeks or months, the plaque can become much harder as the occlusion becomes fibrotic and calcified, making it almost impossible for a guidewire to cross. Failure to cross the obstruction is the primary failure mode for CTO recanalization, and often leads to the abortion of the interventional procedure in favor of a surgical bypass procedure instead, with higher costs and complications.
It is known in the art that when trying to cross an occluded blood vessel with a guidewire, in many cases the guidewire inadvertently deflects into the subintimal space between the intimal layer and the adventitial layer of the blood vessel. Once in the subintimal space, the guidewire can be advanced along side the CTO (which is on the other side of the intimal wall) and beyond the length of the occlusion. Dissection of the blood vessel and guidewire insertion into subintimal space is very common, especially in blocked peripheral blood vessels. The difficulty in many cases is to direct the guidewire back into the blood vessel's true lumen beyond the occlusion so that this new channel can be dilated and used as an internal conduit for blood supply. Known as subintimal recanalization, this procedure can be very useful. There are some advantages to passing around the occlusion, rather than punching directly through it. The subintimal space is more likely to produce a smooth surface for blood flow versus the original lumen, which has remnants of the calcified plaque.
The technique has limited acceptance due to technical challenges of the procedure. Among those who perform subintimal recanalization, there is a technical failure rate of up to 30% due to the inability to reenter the distal true lumen at the specific desired location. Therefore, most clinicians will first try to cross the occlusion. If unsuccessful and if they enter the subintimal space, they will try to reenter the true lumen. If they cannot reenter after several minutes, they will abandon the case and schedule the patient for surgery.
During percutaneous transluminal recanalization, a variety of guidewires are used to pass the occlusion. If the occlusion is hard, a stiff wire is used to cross. Usually the proximal cap of the occlusion is the harder section, and if crossed, then crossing the rest of the occlusion is relative easy.
If during percutaneous extraluminal recanalization via the subintimal approach the true lumen cannot be reentered with guidewire manipulation, a true lumen reentry device must be used. Currently there are two specially designed reentry devices on the market. Published patent applications US20030236542, WO2006105244, US2003120195, and US2006094930 and U.S. Pat. No. 6,081,738 all describe reentry devices and methods, based on curved needle penetration, used with some type of rotational imaging system. PCT patent application PCT/IL2008/000449 describes a reentry balloon catheter that eliminates the needs for rotational orientation and operator direction via imaging guidance. This balloon catheter automatically bends its distal end in the direction of the true lumen. This device eliminates the need for a curved needle, and instead allows direct penetration with or without the support of a straight guidewire or hypotube.